1. Field of the Invention
The present invention relates to an optical storage medium for recording information using marks and spaces, an optical disc drive for recording, reading, or deleting data on the optical storage medium, an optical storage medium inspection apparatus for determining whether the optical storage medium is good or defective, and an optical storage medium inspection method for determining whether the optical storage medium is good or defective.
2. Description of the Related Art
High density, high capacity optical storage media known as DVD, or Digital Versatile Disc, have been developed as a practical high density, high capacity storage medium, and are today widely used as a data medium for handling video and other such large amounts of information. Development of two-layer optical storage media capable of recording to two data recording layers has also been reported by various manufacturers as a means of achieving optical storage media with even greater storage capacity. Development of means for recording as well as reading large amounts of data is also progressing on many fronts with various approaches being used to achieve increasingly higher recording densities. One such approach is the phase-change optical disc drive using a reversible phase change between crystalline and amorphous states.
Japanese Patent Laid-Open Publication No. 2000-200418 teaches technology for recording and reading data by emitting a beam to a phase-change optical storage medium.
FIG. 20 shows the configuration of a common optical system used in the optical pickup head of an optical recording and playback system as an optical disc drive capable of reading and writing data. The semiconductor laser 1 light source emits a linearly polarized divergent beam 70 with an oscillation wavelength λ1 of 405 nm. The divergent beam 70 emitted from semiconductor laser 1 is converted to parallel light by a collimating lens 53 with a 15 mm focal length, and is then incident to a diffraction grating 58. The divergent beam 70 incident to the diffraction grating 58 is split into three beams of orders 0 and +/−1 diffracted light. The order 0 diffracted light is the main beam 70a for data recording and playback, and the order +/−1 diffracted beams are the two sub-beams 70b and 70c used when detecting the tracking error (TE) signal by a differential push-pull (DPP) method for stably detecting the TE signal. The diffraction efficiency ratio of the diffraction grating between the zero order beam and one first order beam is normally set from 10:1 to 20:1 in order to avoid unwanted recording by sub-beams 70b and 70c, and is here assumed to be 20:1. The three beams produced by the diffraction grating 58, that is, main beam 70a and sub-beams 70b and 70c, pass polarized beam splitter 52, ¼ wave plate 54, and are converted to circular polarized light which is then converted to a convergent beam by objective lens 56 with a 3 mm focal length and focused on the data recording layer 40b through transparent layer 40a of the optical storage medium 40. The aperture of the objective lens 56 is limited by aperture 55 to a 0.85 numerical aperture (NA). The transparent layer 40a is 0.1 mm thick. The optical storage medium 40 has a data recording layer 40b and transparent layer 40a. The data recording layer 40b is a semi-transparent film and only part of the incident beam passes. The beam that passes the data recording layer 40b is used for reading and writing data to data recording layer 40c. 
FIG. 25 shows the track configuration of an optical storage medium 40 according to the prior art. This optical storage medium 40 is an optical storage medium having a recording area in a groove-shaped track (groove track 1301) with the groove track formed in a continuous spiral.
FIG. 21 shows the relationship between a beam and the track on the data recording layer 40b. A continuous groove is formed as the tracks, identified as tracks Tn−1, Tn, Tn+1, of the optical storage medium 40. The track period Tp is 0.32 μm. The laser beam is positioned so that when the main beam 70a is on a track, sub-beams 70b and 70c are between tracks. That is, the distance L between the main beam and sub-beams in the direction orthogonal to the track is 0.16 μm. As with DVD media, data is recorded using 8-16 modulation, that is, using marks and spaces having a length that is an integer multiple of T based on period T where the length of the shortest mark and the length of the shortest space is each 3T. The shortest mark length is 0.185 μm.
The main beam 70a and sub-beams 70b and 70c reflected by the data recording layer 40b pass objective lens 56 and ¼ wave plate 54, are converted to linear polarized light 90 degrees to the incoming path, and reflected by the polarized beam splitter 52. The main beam 70a and sub-beams 70b and 70c reflected by the polarized beam splitter 52 are converted to convergent light as they pass through collective lens 59, pass cylindrical lens 57 and are incident to photodetector 32. Astigmatic aberration is added to main beam 70a and sub-beams 70b and 70c when they pass cylindrical lens 57.
As shown in FIG. 22, the photodetector 32 has eight receptors 32a to 32h with receptors 32a to 32d detecting the main beam 70a, receptors 32e, 32f detecting sub-beam 70b, and receptors 32g, 32h detecting sub-beam 70c. Receptors 32a to 32h respectively output current signals I32a to I32h according to the detected light quantity.
The focus error (FE) signal from the astigmatic aberration method is obtained as(I32a+I32c)−(I32b+I32d).
The TE signal from the DPP method is obtained as
{(I32a+I32c)−(I32b+I32d)}−a*{(I32e−I32f)+(I32g−I32h)} where a is a coefficient dependent on the diffraction efficiency of the diffraction grating and is here 10.
The data (RF) signal recorded to the optical storage medium 40 isI32a+I32b+I32c+I32d.After amplification to a desired level and phase compensation, the FE signal and TE signal are supplied to actuators 91 and 92 for focusing and tracking control.
The eye pattern of the RF signal is shown in FIG. 23. The data recorded to optical storage medium 40 is obtained by inputting the RF signal to a transversal filter and emphasizing the high frequency band, digitizing the signal, and then demodulating the digital signal. Because 8-16 modulation produces DC-free code, the binarization threshold value SL can be easily set to the center of the eye by integrating the 1s and 0s of the binarized signal by time and applying a differential operation.
A phase-change type optical disc drive emits a semiconductor laser to the optical storage medium using two power levels, a peak power level for changing the recording layer from crystalline phase to amorphous phase, and a bias power level for changing it from amorphous phase to crystalline phase, thereby forming amorphous marks on the optical storage medium and crystalline spaces between the marks to record digital information. The reflectivity of these marks and spaces differs due to the difference of the crystalline state of the marks and spaces, and this difference in reflectivity is used during playback to read the recorded signal.
FIG. 24 shows the configuration of a phase-change type optical disc drive according to the prior art. As shown in FIG. 24 this optical disc drive has an optical pickup head 1202 for emitting a laser beam to the optical storage medium 40 and receiving light reflected from the optical storage medium 40, a playback means 1203, playback signal quality detector 1204, optimal recording power determination means 1205, recording means 1208, laser drive circuit 1207, and recording power determination means 1206.
After the optical storage medium 40 is loaded in the optical disc drive and specific operations for identifying the media type and rotation control are completed, the optical pickup head 1202 moves to an area for setting the optimal recording power. This area is a predetermined area at the inside or outside circumference of the disc outside of the user area where user data is recorded. The peak, bias, and bottom power levels are determined for phase-change media, but a method for determining the peak power is described here.
Initial peak power and bias power levels are set in the laser drive circuit 1207 by the recording power determination means 1206. The recording means 1208 then sends a signal for recording one groove track to the laser drive circuit 1207, and the signal is recorded by the optical pickup head 1202. The output beam of the semiconductor laser part of the optical pickup head 1202 is focused as a light spot on the optical storage medium 40 at this time to form a recording mark according to the beam emission waveform. When recording is completed the semiconductor laser of the optical pickup head 1202 emits at the read power level to play back the track that was just recorded, and a signal 1209 that varies according to the presence of these recording marks on the optical storage medium 40 is input as the playback signal to the playback means 1203. A playback signal process including amplification, equalization, and digitizing is then applied to this playback signal 1209 by the playback means 1203, and the resulting signal 1210 is input to the playback signal quality detector 1204.
The playback signal quality detector 1204 detects the signal quality of signal 1210 and the result is input to the optimal recording power determination means 1205.
In this example the playback signal quality detector 1204 detects jitter when the recorded signal is reproduced. FIG. 26 shows the relationship between peak power and jitter. Peak power is shown on the horizontal axis and jitter on the vertical axis in FIG. 26. If the playback conditions are equal, a lower jitter level indicates accurate recording. The detection result, i.e., signal quality, is therefore determined OK if jitter is less than or equal to a set threshold value, and no good (NG) if above this threshold value.
The optimal recording power determination means 1205 operates according to a flow chart such as shown in FIG. 27.
(a) If the first result of the playback signal quality detector 1204 is NG, the peak power is reset to a level higher than the initial setting (step 1505).
(b) If the result of the playback signal quality detector 1204 is OK, the peak power is reset to a level lower than the initial setting (step 1504).
(c) The groove track is again recorded at the set peak power level and then read (step 1506).
(d) If the first result from the playback signal quality detector 1204 is NG and the second result is OK, the optimal recording power determination means 1205 sets the optimal recording power to the average of the current peak power setting and the previous peak power setting plus a specified margin (step 1511).
(e) If the first result from the playback signal quality detector 1204 is OK and the second result is NG, the optimal recording power determination means 1205 sets the optimal recording power to the average of the current peak power setting and the previous peak power setting plus a specified margin (step 1511).
With the conventional configuration described above, however, the I3pp/I4pp ratio between the signals obtained from data recording layers 40b and 40c is 15% and 20% and jitter is 10% and 8%, respectively, and in each case the characteristics of signals read from data recording layer 40b are worse than those of signals read from data recording layer 40c. This means that recorded data cannot be read with high reliability unless the recording density of data recorded to data recording layer 40b is lower than the recording density of data recorded to data recording layer 40c. 
Furthermore, the area for determining the optimum emission power is generally different from the user area for recording user data. As a result, warping of the optical storage medium and variations in pickup head installation can produce a relative tilt between these two areas, and user data may be recorded at a lower effective power level than the emission power determined in the area for determining the optimum recording power. Conversely, user data may be recorded at a higher effective power level than the emission power determined in the area for determining the optimum recording power. The prior art described above determines the optimum power level based on the jitter detected after recording a random signal, but because the signal quality of the shortest mark has the greatest effect on jitter, the optimal power level for the shortest marks is actually determined. While data can therefore be correctly recorded with the shortest marks even if the recording power fluctuates somewhat, the effect of power fluctuation cannot be ignored for marks longer than the shortest marks particularly if the recording density increases, and recorded signal quality can deteriorate.
Furthermore, if relative tilt between the optical storage medium and head or defocusing occurs during playback, the playback signal quality drops for signals read from marks longer than the shortest mark, and it may not be possible to correctly reproduce the data.
The present invention is directed to solving these problems of the conventional optical disc drive, and a first object of the invention is to provide an optical storage medium and optical disc drive that can record or reproduce data with high reliability even when the data recording density is the same on two data recording layers.
A second object of the invention is to provide an optical storage medium and optical disc drive that can record or reproduce data with high reliability even using an optical storage medium in which jitter from the shortest marks and spaces is worse than jitter from marks and spaces longer than the shortest marks and spaces.
A third object of the invention is to provide an optical storage medium and optical disc drive that can correctly record or reproduce data even when defocusing or relative tilt between the optical pickup head and optical storage medium occurs during recording or playback.